Friday, June 05, 2009

Frigid Friday with frost tonight

An unseasonably cool airmass has pushed into southern Manitoba today with gusty northwest winds advecting Arctic air from the north. Morning temperatures in Winnipeg were a chilly +2C, feeling even colder with northerly winds of 30 to 50 km/h. Sunshine with will mix with clouds today but temperatures will struggle to hit double digits this afternoon. Normal highs for this time of year are 23C. Note that the cold winds coming off the lakes are even generating some lake effect showers mixed with snowflurries this morning off the south end of Lake Winnipeg through the Grand Beach to Beausejour areas as seen in the radar image to the left (snowflurries reported in the Tyndall area this morning!)

For tonight, a ridge of high pressure over southern SK will build into southern MB bringing clearing skies and light winds. This will bring a widespread freeze across southern MB tonight into early Saturday morning with temperatures dropping to the zero to -2C range. Cover or bring in those tender annuals! Saturday will be a little nicer than today with sunshine, light winds and temperatures near 15C.. still a good 8C below normal. Increasing clouds are expected by Sunday with a chance of showers Sunday night through Tuesday.

Only hope for avoiding frost overnite would be low level clouds to continue streaming off the lakes. 850 hPa temps modify somewhat to -2 C so 'advective' freeze' in the above scenario seems unlikely.

Low level cold (and dry air) advection will persist and undercut increasing mid level warm and moist advection moving up from the Dakotas. 700 hPa 'warm front' and associated higher clouds looks to protect areas SW of an Estevan to Fargo line tonite. By dawn Sunday, the front should be in our region with dry ENE flow at low levels.

Lobe of Polar Vortex over Alberta will phase in with large cut off low in California (GFS has long advertized this). Two shortwaves will be ejected. LLJ of first disturbance focused well to the south over central plains on Sat nite. Upper flow then turns sharply SW and will focus second wave and LLJ further north... WC Central Minnesota may be in line for heavy precip (but not severe weather).

We look to stay high and dry as dry easterly flow suppresses any precip until possibly the upper low wobbles in Monday and Tuesday. However, with moisture cut off well to the SE by surface low and coolest temps aloft in the Dakotas... we may just end up clouds and a few sprinkles. Dreary, cold, and on top of that boring. I can understand this happening in January, but in June... sheesh.

Visible satellite showed most low clouds were cellular in nature and dissipating. Exception was solid bank from Winnipeg Beach off to NNW. These clouds appear to be hanging tough after sunset and are slowly advecting south.

At the same time, high clouds associated with warm air advection aloft were streaming in just south of the TransCanada. If anything they are a bit further north than progged by GFS. Seems like there will be an unlucky zone between the low stratus and higher cirrus clouds... question is where will this set up exactly. Do you think that bank of low clouds will reach Winnipeg Rob?

That deck of low cloud just north of Winnipeg is still hanging together and ever so slowly edging south towards Winnipeg. Not sure if it will make it to the city, but it may save us from a long duration freeze tonight if it does. As it stands now (11 pm) temperature is down to 2C at YWG airport, but 0c values already noted in northern suburbs. A little milder here in the south end at 4.5C with a light northerly wind off the city.